Conventionally, there has been a compressor including a cylindrical-shaped screw rotor which rotates about a center axis and which has in its outer circumferential surface at least one groove portion extending spirally about the center axis, and gate rotors which rotate about a center axis and which have a plurality of tooth portions arrayed circumferentially on its outer circumference, the groove portion of the screw rotor and the tooth portions of the gate rotors being engaged with each other to form a compression chamber (see JP 2-5778 A).
That is, this compressor is a so-called CP-type single screw compressor. The term ‘CP-type’ means that the screw rotor is formed into a cylinder-like shape while the gate rotors are formed into a plate-like shape.
Then, the gate rotor center axis is parallel to a plane orthogonally intersecting with the screw rotor center axis. That is, the tooth portions of the gate rotor are engaged with the groove portion of the screw rotor along the screw rotor center axis.
With a view to preventing interferences between the screw rotor and the gate rotor, side faces of the gate rotor tooth portions are given a maximum angle and a minimum angle each of which is formed by a gate rotor tooth-portion side face and a screw rotor groove wall surface on a plane which orthogonally intersects with the gate rotor plane and which contains a rotational direction of a tooth center line of the gate rotor (hereinafter, angles given by the maximum angle and the minimum angle will be referred to as edge angles of the gate rotor; see edge angles δ1, δ2 of FIG. 13).